Turbocharger systems for supercharging diesel-type internal combustion engines, preferably for heavy-duty vehicles, usually include a single-stage compressor driven by a single-stage turbine, both of the radial type. Turbocharger systems with two-stage supercharge sometimes also include intermediate cooling, but the construction is usually based on standard assemblies intended for single-stage supercharging.
Superchargers suitable for a diesel engine of 6 to 20 liters cubic capacity normally have an efficiency, under stationary conditions, of between 50% and 60% (ηcompressor*ηmechanical*ηturbine). In contemporary diesel engines, the efficiency benefit is lower than for future engines, which will require higher charging pressure. Examples of systems which raise the supercharging requirement are exhaust gas recirculation for lower nitrogen oxide emissions or systems offering variable control of inlet valves.
Turbocharger systems with higher efficiency than 60%, under stationary conditions, offer a greater prospect of meeting future demands for environmentally friendly and fuel-efficient engines. Until now, environmental demands upon diesel engines have usually led to worsened efficiency, which has therefore meant that the energy resource of the fuel has not been well utilized.